Fertilizer efficiency has become a major issue in the world. The major element of fertilizer is nitrogen (N). In one study, using data from over 800 experiments, it was estimated that only 51% of the N applied was recovered by cereals plant (Dobermann and Cassman 2005). In another study, it was reported that average N recovery in cereals in China was 30-35% (Fan 2004). Phosphorous is the second largest element in fertilizer compositions and its efficiency is even lower. It was estimated to be around 10-25% (Linsay 1979). Potassium is the third largest fertilizer composition and its efficiency is around 40% (Baligar V C 1986).
One of the main factors for the low efficiency of fertilizers is due to the excellent water solubility of many of its components. In practice, fertilizers are often just applied once at the beginning of the growing season. After the application, nutrients from fertilizers are dissolved in water and released to soil in amounts that are too much for plants to absorb. The unabsorbed nutrients can be leached to the environment, and find their way to surface water such as ponds, lakes and rivers or continue to leach into the sub-surface water table contaminating many of the rural community water supplies. Low efficiency of fertilizer not only increases the cost of fertilization, but also contributes significantly to environmental pollution. In the case of nitrogen based fertilizers, one of the major mechanisms for its poor efficiency is the impact of biologically driven processes on water solubilized sources of nitrogen. Urea is the main component of most nitrogen fertilizers. In the presence of soil moisture, natural or synthetic ureas are dissolved and are converted to ammonium ion by bacterial activity, making the nitrogen available for plant uptake. Ammonium can be further converted by bacteria in soil to nitrate through a process called nitrification. Nitrate is also available for plant uptake. Excess ammonia not absorbed by plants can leach into water which can be toxic to water creatures (US EPA822-R-13-001). Excess nitrates can also leach into water, causing the increasing of nitrate concentration in the ground water. Consumption of nitrate contaminated water by human can cause methemoglobinemia (blue baby syndrome) (Kross, Hallberg et al. 1993). Moreover, excessive nitrate can be converted into nitric oxide or nitrous oxide by certain types of bacteria in the soil, through a biological process called denitrification. Nitrous oxide is a potent greenhouse gas, whose potency on global warming is 300 times stronger than carbon dioxide (http://epa.gov/climatechange/ghgemissions/gases/n2o.html). In the case of phosphate fertilizer, phosphate fertilizer in the soil can be eroded into the river causing eutrophication, which can pose severe damage to the whole water body (Bennett E M 2001). Over usage of potassium fertilizer has been associated with deterioration of soil structure. The other problem associated with the over usage of potassium fertilizer is the disruption of the balance of nutrients in the soil such as Ca, Fe and Zn, that are in a plant available form (S 2012).
The goal of the worldwide agricultural industry is to increase the efficiency and decrease the environmental impact of fertilizer. One method is to apply the fertilizer in small doses but with more frequency. However, this approach will incur increased labor cost and is not economically practical, especially in developed countries, where the labor cost tends to be higher. A preferred method is to slow down the dissolution of water soluble fertilizer components and extend the period of time for release of nutrients in a plant available form. The current technological trend for slowing dissolution of fertilizer is focused on inventions that utilize various types of coatings which control water's access to the fertilizer's water soluble components. While many inventions claim the ability to coat any of the fertilizer components, the major commercialized coating-based products are centered around urea. To implement these inventions usually require separate process steps, heat and specialized application equipment for application of coatings to fertilizer. The choice of coating urea is based on (1) Urea is usually produced through a synthetic process making the additional steps of coating conveniently part of the overall urea preparation process, (2) urea is one of the more costly as well as one of the largest components in a fertilizer formulation and (3) urea bonds well with most organic coatings versus the inorganic nature of the other components of fertilizer. The core of the technology is that coating urea prills (granules) with a water-insoluble, semipermeable, or impermeable (with pores) material delays the release of N from the urea. Urea is highly soluble in water, but the solubility of coated urea is dependent on the coating material, its thickness, and the coverage and uniformity of the coating on the granule.
The first widely used urea coating technology is a sulfur coating in U.S. Pat. No. 3,342,577 (Blauin) which demonstrates a process of sulfur coating of urea particles to slow dissolution. It was developed in the late 1960's by the Tennessee Valley Authority (TVA) as an economical system for reducing the rate of dissolution when urea particles are applied to the soil as fertilizer. The release of nutrients from sulfur-coated fertilizers occurs by diffusion of water through imperfections in the sulfur coating and through coating breakdown. In this technology, urea is coated with molten sulfur. It is sometimes topped with a coating of wax to overcome the numerous granule surface imperfections as well as to mitigate damage to the coating through processing, packaging, storage and transport of the coated urea. Sulfur is water impermeable, but the cracks on the surface allow water to penetrate in the beginning. Overtime, sulfur is degraded by bacteria in the soil and urea is totally released (Christians 2004).
Attempts to seal the sulfur coating have been described in U.S. Pat. No. 5,219,465 (Goertz), by utilizing a polymethylene poly(phenyl-isocyanate), a catalyst to promote polyurethane curing with polyester polyols to topcoat the sulfur on the surface. U.S. Pat. No. 5,599,374 (Detrick) relates to a process for producing sulfur-coated, slow release fertilizers having a uniform, durable polymeric coating over the sulfur-coating which improves impact and abrasion resistance properties. This polymer coating is formed by the direct in situ co-polymerization of diethylene glycol-triethanolamine polyol and a diisocyanate on the surface of the sulfur-coated urea granule.
U.S. Pat. No. 5,653,782 (Stern et. al.) describes a process by which fertilizer particles are preheated to a temperature in excess of the melting point of sulfur (115° C.), prior to being mixed with solid sulfur pills. The resulting fertilizer is comprised of fertilizer particles contained in a sulfur matrix.
U.S. Pat. No. 6,338,746 (Detrick et al.) describes a process of first coating a fertilizer with a polymer, then coating the polymer with sulfur and thereafter applying a polymer coating.
U.S. Pat. Application, 20100011825 (Ogle, et al.) teaches that multiple layers of coating for urea granules in which the urea is coated with a polymeric layer, an intermediate layer and sulfur layer outside.
While sulfur represents a low cost coating, it still required separate manufacturing steps, high temperatures (>120 C) and is not attrition resistant during processing, packaging, storage and transporting without the addition of other additives.
Urethane polymer technologies have also been developed to coat urea fertilizer, which allows more precise rate of nitrogen release than sulfur coated urea. U.S. Pat. Nos. 3,264,089 (Hansen) and 3,475,154 (Kato) inventions involve preformed polymers in quick drying solvents. As these solvents are flashed off, their fumes create a low flash point hazard and can result in pinhole imperfections on the coated fertilizer. Isocyanate based polymers are utilized in a number of inventions which are based on a plurality of coatings in which a urethane polymer is formed on the surface of a fertilizer particle through separate coating of an isocyanate capable of crosslinking with compounds having multiple active hydrogens such as polyols or polyamine. Most inventions also include a final coating that is hard but not brittle to improve resistance to damage to the coatings during processing, packaging, storage and transport.
U.S. Pat. No. 5,538,531 (Hudson et al.) describes controlled release fertilizers and a method for their production. These controlled release fertilizers have a central mass of particulate fertilizer which contains at least one water soluble plant nutrient surrounded by a plurality of coatings. The inner coating comprises the reaction product of an aromatic, a polyol having from 2 to 6 hydroxyl units and at least one alkyl moiety containing from about 10 to 22 carbon atoms. An outer coating of a wax is also necessary.
U.S. Pat. No. 5,803,946 (Petcavich, et al.), teaches a urea particulate plant nutrient having on its surface an interpenetrating polymer network comprising a biuret, a urethane and tung oil.
U.S. Pat. No. 6,663,686 (Geiger et al.) teaches a process in which wax is used as a component of the polyurethane coating, not as a separate over-coat. The invention describes controlled release can be achieved with less coating materials and by a relatively simple procedure which in turn, permits the reduction of coat thickness.
U.S. Pat. Application, 20040016276 (Wynnyk, et al.), utilizes an isocyanate and castor oil to build a urethane polymer for control release of the water soluble components of fertilizer and incorporates an inorganic and/or an organic particulate filler and, optionally, a wax in a one-step coating process. The addition of the particulate filler is touted as improving processing, handling, packaging and transport.
While many of these inventions have been shown to slow down the dissolution of urea, the processes, equipment and chemistries result in a coated urea that is very expensive when compared to uncoated urea and is mainly used for expensive crops and turf industry (LAL 1998). Many of these coatings also provide no nutritional value for plants.
Although the listed inventions claim to provide a coating to limit dissolution of other fertilizers components such as phosphorus, potassium and micronutrients, the cost of the application of such technologies has impaired their entry into the agricultural marketplace. While many of the coating technologies have strategies to overcome the attrition of coverage of the urea particle, the inorganic nature of the other fertilizer components causes difficulties in the adhesion of the coatings to the inorganic particles. Natural based fertilizers such as manure are also not coated due to the cost of the coating operations, the quick loss of nitrogen value due to existing bacteria population and manure's amorphous physical nature.
Patent CN104803807 (Yuan) teaches us that urea, ammonium phosphate, potassium chloride, diammonium phosphate, monoammonium phosphate, potassium nitrate, potassium dihydrogen phosphate, magnesium humate, zinc humate, urea ion humate or nitro humic acid granules can be coated with dicyclopentadiene, glycerol ester copolymer, polyvinyl alc., and PMSM (p-methylstryrene-maleic anhydride copolymer).
Patent CN 104609983 (Li, et al.) teaches us that a hydrophobic film is formed on the surface of fertilizer granules by in situ reaction of polymethylene polyphenyl polyisocyanate and polyether polyol.
Patent CN 104446875 (Chen, et al.) teaches us that polycondensation reaction of citric acid, polyglycolic acid and potassium carbonate can form a slow releasing potassium fertilizer.
While all these technologies can slow down the dissolution of water soluble inorganic fertilizer components, the cost of the specialized equipment, chemistries and processing to produce the coated particle and the attrition of the coating coverage during processing, packaging, storage and transport has severely limited their utility for agriculture. Moreover, all these fertilizer must be made according to certain specifications in large volume and cannot be tailored to customer's specific needs. In light of the above, it is desirable to develop a slow release fertilizer coating technology which is environmental-friendly, low cost and can be applied with simple application equipment such as mixers blenders or tumblers. Moreover, this technology should be flexible enough to prepare small batches according to the customer's needs.
U.S. Pat. No. 9,440,890 (Gabrielson) teaches reaction products may be formed from the reaction of formaldehyde, DCD, urea, and an ammonia source in water which may be included in agricultural products, including fertilizer compositions and nitrification inhibitor systems. Gabrielson also states that fertilizer compositions that include the reaction product can be beneficial for reducing leaching of nitrification inhibitors applied to soil. However, the reactions are performed in an aqueous medium which limits their applications to systems or processes not negatively impacted by the presence of water. Gabrielson's invention also requires other formaldehyde reactive constituents such as urea and ammonia which have excellent water solubility to assist with the dicyandiamide (DCD) since DCD has a limited solubility in water of approximately 32 grams/liter at 20° C. resulting in slower reactivity and low concentrations of the resulting polymers and oligomers. The resulting composition of the reaction product is reported to be a mixture of a triazonyl-formaldehyde-DCD adduct, a urea-formaldehyde-DCD adduct, and a DCD-formaldehyde-oligomer adduct. In fact, the reported composition of the formaldehyde reaction product comprises only about 0.1 to 10 wt. % of a DCD-formaldehyde-oligomer adduct based upon the weight of the nitrification inhibitor system. Since the described invention requires water as a reaction medium and due to research reports that the presence of water is essential in driving the degradation of dicyandiamide to diaminomethylene ureas as shown in the following reaction,
the loss of the cyano-group would diminish the product's nitrification inhibition capabilities either directly or in a slow release mechanism that is dependent on microbial activity to break down the polymer/oligomer releasing dicyandiamide over time. Earlier work in U.S. Non-Provisional application Ser. No. 15/641,264 (McKnight) filed Jul. 4, 2017 (to which the present invention claims priority) discussed the use of an aprotic non-aqueous organo solvent delivery system NOSDS comprising one or more aprotic solvents that can serve as the reaction medium for the formation of biodegradable, hydrophobic polymers that are the reaction product of aldehyde(s) and nitrogen containing compounds. McKnight also detailed a process wherein said biodegradable, hydrophobic polymer involves 1) dissolving the nitrogen containing compound into an aprotic NOSDS at temperatures of 10-140° C. wherein the composition is cooled to 30-60° C. 2) the aldehydes are charged at a rate that controls the exotherm with 5-20° C. of the reaction temperature that is 30-90° C. in a molar ratio of aldehyde to aldehyde reactive sites on the nitrogen containing compound of (0.10-0.90)/1.0. 3) The reaction is held at 30-70° C. and at a pH of 7.5-10.0 for 5 to 12 hours until the free formaldehyde is 40,000 to 5,000 ppm's. 4) The reaction is heated to 70-100° C., the pH is adjusted to 4.0-8.0 and held until free formaldehyde is <700 ppm, wherein the composition is cooled to less than 40° C. and packaged. McKnight also stated that the resulting biodegradable, hydrophobic polymer dispersed within the aprotic NOSDS imparted good water resistant properties to urea. However, it has been determined that the reaction conditions to produce these biodegradable polymers/oligomers were too aggressive for cyano-containing nitrification inhibitors resulting in the conversion of the cyano-group to an amide group impacting solubility and most importantly, nitrification inhibition.
Thus, there is a need to for compositions and an improved method of making liquid fertilizer additives of biodegradable polymers and/or oligomers comprised of the reaction products of aldehyde(s) with cyano-containing nitrification inhibitors that have one or more aldehyde reactive groups.